Method of manufacturing a crank shaft for a hermetic reciprocal compressor

ABSTRACT

A method of manufacturing a crank shaft for a hermetic reciprocal compressor including the steps of providing a main shaft and a crank portion eccentric for a predetermined degree from the main shaft that are separately formed. The main shaft and the crank portion are joined through laser welding. The main shaft is a hollow pipe and the crank portion is made by sintering. The main shaft and the crank portion are connected, and an end portion of the main shaft is inserted into an annular groove formed at a main shaft connection side of the crank portion. Accordingly, the main shaft is a drawn steel pipe, and the crank portion is formed by sintering, thus the crank shaft becomes lighter and no post-process is needed. Therefore, the manufacturing process is remarkably reduced, and the crank shaft manufactured at a lower production cost.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a method ofmanufacturing a crank shaft for a hermetic reciprocal compressor, andmore particularly to such a method in which the crankshaft productioncosts are improved and productivity is reduced.

[0003] 2. Description of the Related Art

[0004] It is well known that a hermetic reciprocal compressor has anelectric driving portion and a compressing portion in a case. Rotationalmovement of the electric driving portion is converted into thereciprocal movement of the compressing portion by a crank shaft, andthus, as a piston of the compressing portion is reciprocally moved in acylinder, refrigerant is compressed.

[0005]FIG. 1 shows a conventional hermetic reciprocal compressor. Asshown in FIG. 1, the conventional hermetic reciprocal compressor has anelectric driving portion 20, and a compressing portion 30 disposed inthe case 10 having an upper shell 1 and a lower shell 2. The electricdriving portion 20 and the compressing portion 30 are connected to eachother by the crank shaft 40. The rotational movement of the electricdriving portion 20 is converted into the reciprocal movement of thecompressing portion 30 by the crank shaft 40.

[0006] The crank shaft 40 comprises a main shaft 41 inserted into arotor 21 of the electric driving portion 20, and a crank portion 42connected by the piston 31 and a connecting rod 32 of the compressingportion 30. In FIG. 1, reference numeral 22 represents a stator, 33 is acylinder block, and 34 is a cylinder head.

[0007] The conventional method for manufacturing the above-describedhermetic reciprocal compressor is to mold the crank shaft by casting.After molding, the molded crank shaft is processed to a desired size. Inother words, parts of the forged surface of the molded crank shaft areremoved by cutting such as by rough cutting and turning. Next, toincrease the toughness of the crank shaft, it is put through aheat-treatment process. The heat-treated crank shaft is again clean cutand processed to provide the final crank shaft.

[0008] However, the conventional method of manufacturing the crank shaftdescribed above does not offer a simple process for producing thefinished molded product. In this process, the molded product needs to bepost-processed by processing such as by rough cutting, turning, andgrinding. This lowers productivity and increases manufacturing costs.

[0009] Additionally, since the amount of material that is cut increasesas casting dispersion increases, the cycle time also increases, therebycausing low productivity. Moreover, since the dispersion is great, loadconditions are different when processing and abrasion of the cuttingtools are increased.

[0010] Furthermore, it is difficult to use the conventional method ofmanufacturing a crank shaft to manufacture a crank shaft which ishollow, which allows for increased toughness, greater than the toughnessof the conventional crank shaft. Moreover, the conventional solid crankshaft, being solid, is heavy. Consequently, the efficiency of thecompressor is lowered with a solid crank shaft because of the reciprocalmotion of a heavier mass.

[0011] Lastly, in the conventional method for manufacturing the crankshaft, a deep oil passage is formed in the molded product through apost-process. Thus, this step also lowers the productivity inmanufacturing the crank shaft due to the complexity of processing of theoil passage.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a method ofmanufacturing a crank shaft for a hermetic reciprocal compressor capableof improving productivity and reducing production costs, therebyeliminating the need for initial cutting and post-processes, andsimplifying the manufacturing process to form an oil passage.

[0013] Another object of the present invention is to provide a methodfor manufacturing a crank shaft, which having reduced weight.

[0014] In the method of manufacturing a crank shaft according to thepresent invention, a main shaft and a crank portion eccentric for apredetermined degree from the main shaft are separately made. The mainshaft and the crank portion are then joined through laser welding. Themain shaft is a hollow pipe and the crank portion is made through sintermolding. The material of the hollow pipe and the sinter molded productis a metallic alloy including less than 0.5% carbon by weight percent.It is preferable that the hollow pipe be a carbon steel pipe.

[0015] An annular groove for embracing an end portion of the main shaftis formed at the connection side of the crank portion, and the crankportion and the main shaft are connected with each other so that the endportion of the main shaft is inserted into the annular groove of thecrank portion. Here, the annular groove is formed so that the main shaftcan transition-fit relative to the annular groove.

[0016] According to the preferred embodiment of the present invention, amethod of manufacturing a crank shaft for a hermetic reciprocalcompressor having a main shaft and a crank portion which is eccentricfor a predetermined degree from the main shaft, comprises the steps of:preparing the hollow pipe main shaft by drawing and cutting a carbonsteel pipe of a predetermined length, and forming at least one oilpassage in the carbon steel pipe; preparing the crank portion forming amolded product having an eccentric shaft and a weight balancer bysintering a metallic alloy powder, and then forming at least one oilpassage in the molded product, and forming an annular groove at one sideof the molded product for a predetermined depth; joining the main shaftand the crank portion by using a laser welder after inserting an endportion of the main shaft into the annular groove of the crank portion;forming an oxide coating on the joined crank shaft for increasedcorrosion and abrasion resistance of the joined crank shaft; and finalclean cutting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The object and features of the present invention will become moreapparent by describing the preferred embodiment of the present inventionby referring to the appended drawings, in which:

[0018]FIG. 1 is an exploded perspective view showing a conventionalhermetic reciprocal compressor;

[0019]FIG. 2 is a cross-sectional view showing the method ofmanufacturing a crank shaft of a hermetic reciprocal compressoraccording to the present invention; and

[0020]FIG. 3 is a perspective view showing a crank shaft of a hermeticreciprocal compressor manufactured according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] Hereinbelow, the preferred embodiment of the present inventionwill be described in greater detail by referring to the appendeddrawings.

[0022]FIG. 2 is a cross-sectional view showing the method ofmanufacturing a crank shaft for a hermetic reciprocal compressoraccording to the present invention. FIG. 3 is a perspective view showinga crank shaft of an assembled hermetic reciprocal compressormanufactured according to the present invention.

[0023] As shown in FIGS. 2 and 3, the crank shaft, 40 manufacturedaccording to the method of the present invention, comprises a main shaft41 and a crank portion 42 extending in an eccentric direction for apredetermined amount from the main shaft 41. The main shaft 41 and thecrank portion 42 are joined through laser welding.

[0024] The main shaft 41 is a hollow pipe. In the preferred embodimentof the present invention, a drawn carbon steel pipe is cut to apredetermined length, and at least one oil passage 41 a is formed at apredetermined place through the cut carbon steel pipe. When the mainshaft 41 comprises a hollow pipe, the weight is greatly reduced ascompared to a solid shaft. Moreover, straightness of the hollow pipe isimproved and dispersion, or flaring of the end of the cut pipe, isconstant, thus there is no need to have an initial cutting process.

[0025] In the meantime, a carbon steel pipe for an automobile or amachine is used for the main shaft 41 in the preferred embodiment of thepresent invention. Yet, it is not limited to the above example. The mainshaft 41 may be formed of a hollow pipe made of metallic alloy includingless than 0.5% carbon.

[0026] The crank portion 42 has an eccentric shaft 42 a and a weightbalancer 42 b. The crank portion 42 is formed by a powder metallurgymethod for forming a product by sintering metallic alloy. Here, allkinds of alloy having less than 0.5% carbon may be used as the metallicalloy. Since the crank portion 42 is manufactured as a sintered productby the powder metallurgy method, the process is improved and cutting asa post-process can be omitted. Therefore, the process of manufacturingwill be simplified. Moreover, the crank portion 42 has a holloweccentric shaft 42 a, and at least one oil passage 42 c penetrating fromthe hollow to a back side thereof.

[0027] In addition, the crank shaft 41 has an annular groove 42 d forembracing an end of the main shaft 41 at a connection side of the mainshaft 41. The end of the main shaft 41 is inserted into the annulargroove 42 d of the crank portion 42 and stably connected during thelaser welding of the main shaft 41 and the crank portion 42. The annulargroove 42 d is formed to so that a pipe of a nominal diameter may beinserted.

[0028] After separately forming the main shaft 41 and the crank portion42 as a hollow pipe and a sintering product, and connecting the mainshaft 41 to the crank portion 42 by inserting the main shaft 41 into theannular groove 42 d of the crank portion 42, the main shaft 41 and thecrank portion 42 are joined by laser welding. The welding process isdescribed below in greater detail.

[0029] The main shaft 41 and the crank portion 42 are joined at theconnection portions, where the main shaft 41 and the annular groove 42 dintersect, by laser welding. The welding condition for an optimaltensile strength of the laser welded connection is 3 to 10 Kw of laseroutput, 0.51 to 1.78 m/min of transferring speed, and 20° to 70° ofpoint of focus.

[0030] After laser welding the main shaft 41 and the crank portion 42 inaccordance with the above welding process, an oxide coating is formed atthe surface of the welded members for increasing corrosion proof andabrasion resistance, and a cutting operation is added.

[0031] According to the present invention, the step of rough cutting andturning for adjusting concentricity becomes mostly unnecessary and canbe omitted or minimized. Most of all, productivity is elevated, andsince a laser of high energy density is used, the welding is completedin a short time. Therefore, there is less deformation caused by the heatprocess, and more free design can be done with a non-contact style.

[0032] According to the present invention as described, since the mainshaft of the crank shaft is a drawn steel pipe, the weight is reduced,and also dispersion during the cutting of the pipe end is constant.Thus, there is no need for an initial process. Moreover, as the crankportion is manufactured by sinter molding, the post-process is hardlyneeded and the manufacturing process is significantly reduced.

[0033] Additionally, according to the present invention, as the endportion of the main shaft is connected with the annular groove of thecrank portion inserted thereinto by laser welding, a bead generated fromthe welding fills up the annular groove. Thus, there is no space aroundthe welding area, and density will be increased. Moreover, the weld beaddoes not protrude to the outside, so a post-process for removing theweld bead can be omitted.

[0034] Furthermore, according to the present invention, the main shaftis a pipe shape, thus a simple oil passage is formed in a radialdirection of the main shaft to form the oil passage. Therefore, themanufacturing process will be significantly reduced as compared to theconventional method for forming the oil passage.

[0035] Lastly, the crank portion is formed by sintering, so the degreeof process accuracy is excellent and the post-process can be omitted.

[0036] Consequently, the present invention provides a crank shaft with alow production cost and a high density.

[0037] So far, the preferred embodiment of the present invention hasbeen illustrated and described. However, the present invention is notlimited to the preferred embodiment described herein. The scope of theinvention is set forth in, and only limited by, the following claims.

What is claimed is:
 1. A crank shaft for a hermetic reciprocalcompressor, wherein the crank shaft includes a main shaft connected witha rotor of the hermetic reciprocal compressor; and a crank portioneccentric to a predetermined degree with respect to the main shaftconnected with a connecting rod, and the main shaft and the crankportion being joined to each other through laser welding, after the mainshaft is formed as a hollow pipe, and the crank portion is formed bysinter molding.
 2. The crank shaft of claim 1, wherein material of thehollow pipe and the sintering molded product is a metallic alloyincluding less than 0.5% carbon.
 3. The crank shaft of claim 1, whereinthe hollow pipe is a carbon steel pipe for use in a machine or anautomobile.
 4. The crank shaft of claim 1, wherein an annular groove forembracing an end portion of the main shaft is disposed at a connectionside of the main shaft of the crank portion, and the crank portion andthe main shaft are connected with each other by the end portion of themain shaft being inserted into the annular groove.
 5. The crank shaft ofclaim 4, wherein the annular groove is formed so that the main shaft cantransition-fit relative to the annular groove.
 6. A method formanufacturing a crank shaft for a hermetic reciprocal compressor,comprising the steps of: providing a crank shaft including a main shaftfor connection with a rotor of the hermetic reciprocal compressor; andconnecting a connecting rod to a crank portion of the crank shaft so asto be eccentric to a predetermined degree with respect to the mainshaft, forming the main shaft as a hollow pipe; and forming the crankportion by sinter molding; and laser welding the main shaft and thecrank portion.
 7. The method of claim 6, wherein the hollow pipe and thesinter molded product further comprises a metallic alloy materialincluding less than 0.5% carbon.
 8. The method of claim 6, wherein thehollow pipe is comprises a carbon steel pipe for use in a machine or anautomobile.
 9. The method of claim 6, wherein an annular groove forembracing an end portion of the main shaft is formed at a connectionside of the main shaft of the crank portion; and the crank portion andthe main shaft are connected with each other so that the end portion ofthe main shaft is inserted into the annular groove before the laserwelding step.
 10. The method of claim 6, wherein the annular groove isformed so that the main shaft can transition-fit relative to the annulargroove.
 11. A method of manufacturing a crank shaft for a hermeticreciprocal compressor having a main shaft and a crank portion eccentricto a predetermined degree from the main shaft, comprising the steps of:preparing the main shaft by drawing and cutting a carbon steel hollowpipe of a predetermined length, and forming at least one oil passage inthe hollow carbon steel pipe; preparing the crank portion by forming amolded product having an eccentric shaft and a weight balancer bysintering a metallic alloy powder, forming at least one oil passage inthe molded product, and forming an annular groove in one side of themolded product at a predetermined depth; connecting the main shaft andthe crank portion by inserting an end portion of the main shaft into theannular groove of the crank portion; joining the main shaft and thecrank portion by laser welding the main shaft to the crank portion wherethe two intersect; forming an oxide coating for increasing corrosion andabrasion resistance of the joined crank shaft; and final clean cutting.